Vascular permeability

When exposure is repeated, the allergen binds between two adjacent IgE molecules. This causes release of inflammatory mediators (histamine, leukotrienes, chemotactic factors). These act locally and cause smooth muscle contraction, increased vascular permeability, mucous gland secretion, and infiltration of inflammatory cells (neutrophils and eosinophils). However, histamine can also be released by non-IgE-mediated mechanisms (e.g., due to exposure to certain fungi). 463... 

The human histamine Hi-receptor is a 487 amino acid protein that is widely distributed within the body. Histamine potently stimulates smooth muscle contraction via Hi-receptors in blood vessels, airways and in the gastrointestinal tract. In vascular endothelial cells, Hi-receptor activation increases vascular permeability and the synthesis and release of prostacyclin, plateletactivating factor, Von Willebrand factor and nitric oxide thus causing inflammation and the characteristic wheal response observed in the skin. Circulating histamine in the bloodstream (from, e.g. exposure to antigens or allergens) can, via the Hi-receptor, release sufficient nitric oxide from endothelial cells to cause a profound vasodilatation and drop in blood pressure (septic and anaphylactic shock). Activation of... 

Reliable markers are needed to monitor the activity of antiangiogenic dtugs. Circulating endothelial cells and their progenitor subset are a potential candidate, as is MRI dynamic measurement of vascular permeability/ flow in response to angiogenesis inhibitors, but neither has been clinically validated. 

Fig. 2. IgG-mediated systemic versus local anaphylaxis, a IgG-mediated systemic anaphylaxis. When allergen-IgG immune complexes are formed in the circulation, basophils immediately capture them through IgG receptors on their surface and are activated to release PAF, that in turn act on vascular endothelial cells, leading to increased vascular permeability, b Passive cutaneous anaphylaxis. When allergen-IgG immune complexes are formed in the skin, they stimulate tissue-resident mast cells to release chemical mediators such as histamine, leading to local inflammation. 

Anaphylaxis is the most dramatic and potentially catastrophic manifestation of allergic disorders. It can affect virtually any organ including the cardiovascular system. Cardiovascular collapse and hypotensive shock in anaphylaxis have been attributed to peripheral vasodilation, enhanced vascular permeability and plasma leakage, rather than any direct effect on the myocardium. However, there is increasing experimental and clinical evidence that the human heart is a site and target of anaphylaxis. 

This mediator, apart from aggregating platelets and stimulating many cells types, is a very potent mediator in allergic reactions causing bronchoconstriction with a 1,000 times more potency than histamine. It is able to increase vascular permeability and cause chemotaxis and degranulation of eosinophils and neutrophils [14-16]. 

A variety of molecules are released from cells and plasma proteins during acute inflammation whose net overall effect is to increase vascular permeability, resulting in tissue edema (Table 52—10). 

In the gut, many pathogens adhere to the gut wall and produce their toxic effect via toxins which pervade the surrounding gut wall or enter the systemic circulation. Vibrio cholerae and some enteropathic E. coli strains localize on the gut wall and produce toxins which increase vascular permeability. The end result is a hypersecretion of isotonic fluids into the gut lumen, acute diarrhoea and consequent dehydration which may be fatal in juveniles and the elderly. In all these instances, binding to epithelial cells is not essential but increases permeation ofthe toxin and prolongs the presence of the pathogen. 

Normalization of retinal vascular permeability in experimental diabetes with genistein. Invest Ophthalmol Vis Sci. 42 (9) 2110-14. 

Granger, D.N., McCord, J.M., Parks, D.A. and FloUwarth, M.E. (1986). Xanthine oxidase inhibitors attenuate ischaemia-induced vascular permeability changes in the cat intestine. Gastroenterology 90, 80-84. 

Parks, D.A., Shah, A.K. and Granger, D.N. (1984). Oxygen radicals, effects on intestinal vascular permeability. Am. J. Physiol. 247, G167-G170. 

Diabetes continues to be a major cause of excessive morbidity, severe disability and premature death in Western populations. In developed countries, the cost of diabetes to society may be estimated to be as high as 5% of the total health costs, much of which relates to the chronic vascular complications of this disorder (Williams, 1991). The vascular lesion in diabetes consists of (1) microangiopathy, distinguished by thickening of capillary basement membranes resulting in increased vascular permeability, which is clinically manifested as diabetic retinopathy (Fig. 12.1a) and/or nephropathy (Fig. 12.1b), and (2) macroangiopathy (Fig. 12.2),... 

Th2 lymphocytes are one of the primary factors initiating and perpetuating the inflammatory response.7 In addition, proinflammatory mediators such as the leukotrienes generated during mast cell degranulation can increase vascular permeability, leading to airway edema and increased mucus production.8 Eosinophilic infiltration of the airways is a hallmark of asthma, and activated eosinophils can cause bronchoconstriction and AHR.9... 

Vascular Effects of Complement Activation. During complement activation a number of complement fragments (anaphylatoxins), which are polypeptides with inflammatory properties, are released. The anaphylatoxins C3a and C5a induce smooth muscle contraction and enhance vascular permeability (H31). The most pronounced activation of complement with the formation of anaphylatoxins and terminal C5-9 complexes has been observed in septic shock (B29, B30, P2). Studies indicate that there is a relation between high concentrations of anaphylatoxins and C5-9 complexes and the development of ARDS or MODS in patients with sepsis (H10). 

Thrombomodulin. In patients with SIRS and DIC due to sepsis the serum soluble TM level was higher than in nonseptic and non-DIC patients (A9, B32, G3, II, K7). In experimental ARDS in rats induced by LPS, administration of soluble recombinant TM inhibited the occurrence of intravascular coagulation and prevented the increase in pulmonary vascular permeability (Ul). 

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